The present invention is directed to an automobile speed control system for controlling an automobile at the desired speed, more particularly to a set, memory and cancel circuit arranged in an automobile speed control system for maintaining a constant speed.
In such control systems, the actual speed of an automobile is detected as a pulse frequency and the actual speed signal is obtained by an analog voltage level which is proportional to the pulse frequency. The memory circuit sets or memorizes the actual automobile speed signal at the moment a desired speed set switch is closed. This memorized automobile speed signal is then used as a reference signal by a comparator circuit and on the basis of the difference between the reference signal and the actual automobile speed, the automobile speed control signal system will control the setting of the throttle valve to a position at which the difference will be zero.
In such control systems, the constant speed control operation may be cancelled by the momentary closure of a brake signal switch in order to avoid potential dangers. In order to revert to the automatically controlled constant speed for the operation of the automobile, the driver merely operates a resume switch or set switch in order to close it momentarily. However, when there are obstacles on the road, for instance, when the interval between automobiles becomes too short or when the automobile is about to enter a sharp curve, the driver operates the brake pedal to cancel the constant speed control operation. If the automobile is then driven without the benefit of the constant speed control system for a substantial length of time, the driver will often forget the desired speed that was memorized previously. Thus, when there are no longer any obstacles on the road, the driver can accelerate the automobile to the desired speed. If the driver operates the resume switch to drive the automobile under the control of the constant speed system after the actual automobile speed has exceeded the previously memorized desired speed, the actual speed will be decreased by the constant speed control system to conform the speed to the desired memorized speed. However, if the driver has forgetten that the actual speed is over the previously memorized desired speed at the time the resume switch is operated, the sudden decrease in the actual speed under the control of the speed control system may cause some anxiety to the driver since the driver may feel that the automobile is operating improperly. When the resume operation is performed while the actual speed is under the previously memorized desired speed, the automatic control will cause the automobile speed to increase to the desired memorized speed which does not cause the driver as much concern as the aforementioned situation.